This invention relates to door operators for moving doors, such as overhead garage doors, in either direction between an open position and a closed position. More particularly, the invention relates to door operators including an operating mechanism connected to a door and actuated by a motor for moving the door from one position to another. Specifically, the invention is directed to a revolutionary control system for the motor which simplifies construction and facilitates installation of the door operator.
Since the advent of door operators, various structures have been proposed for the operating mechanism connected to the door and selectively actuated for opening and closing the door. The invention is not directed to improvements in the operating mechanism, which may, for example, take the form of a screw drive, a chain drive, or a cable drive operating mechanism, and can be used in combination with any type of operating mechanism.
Although different motors have been used for actuating door operating mechanisms for opening and closing doors, such as reversible hydraulic motors, spring motors, etc., the reversible alternating current induction motor has found most widespread use, especially in non-industrial installations, such as residential garages. The invention could be used for controlling any type of motor for actuating a door operating mechanism. However, the invention will be described in connection with a door operating mechanism actuated by a reversible induction motor by way of example and not by way of limitation in view of the widespread use of the reversible induction motor.
What the invention does relate to is a control system for whatever motor is used for actuating the door operating mechanism. The control system of the invention is a departure from known control systems and leads to simplification of the mechanical structure of the door operator as well as the procedure by which the door operator is installed. As a result, the door operator is less costly to manufacture, and even a novice can install the door operator with relative ease.
In the past, various control systems have been proposed for door operator motors. The most widely used control systems include a first limit switch which is actuated when the door reaches the open position and a second limit switch which is actuated when the door reaches the closed position. Another switch, positioned between the open limit switch and the closed limit switch and known as a reverse override switch, is preferably included and is actuated shortly before the closed limit switch is actuated for preventing reversal of the door if an obstruction is encountered. Such a control system requires contact-type switches mounted to some structure, such as the door guide rail, cams mounted on the door or the operating mechanism for actuating the switches, and wiring for connecting the switches to the control circuitry. As an alternative, a mechanical follower may be mounted near and driven by the door operator motor. The mechanical follower may take the form of a finely threaded control screw having a threadably engaged cam which is driven along the control screw for actuating open and closed limit switches as well as a reverse override switch mounted near the control screw. In either case, the switches are prone to failure, and, therefore, the control system is unreliable. The switches, cams, and so on are relatively expensive and increase the cost of the door operator. Another drawback is that difficulty can be experienced during installation of the door operator relative to mounting the various switches, and often professional skill is required.
In some prior control systems, use has been made of what is known as obstruction detection or centrifugal switch means for eliminating one or more limit switches. Conventionally, obstruction detection means has been included for sensing when the door encounters an obstruction as the door is opened or closed. If an obstruction, such as an automobile, is sensed as the door is closed, the door operator motor is reversed, and the door is reopened, although, if the door is a predetermined distance or less from the threshold as determined by a reverse override switch, the door is merely stopped. On the other hand, if an obstruction is sensed as the door is opened, the door is merely stopped. If use is made of the obstruction detection means for eliminating one or more limit switches, when the door reaches the limit position, the obstruction detection means is relied upon for de-energizing the door operator motor. Of course, if the door is not to be reversed when the door reaches the closed position, a reverse override switch must be included which has the concomitant disadvantages discussed above relative to switch failure, expense, difficulty of installation, and so on. Furthermore, if limit switches are eliminated and use is made instead of the obstruction detection means, every time the door is open or closed, the door is rammed forcibly against a mechanical stop or the threshold which mechanically stresses the operating mechanism, the door mounting structure, and the door, and significantly increases maintenance as well as shortens the life of the door operator, the door mounting structure, and the door.
Furthermore, after installation of the door operator, adjustment of the position of the closed limit, the open limit, and/or the reverse override switches may be required which has the same attendant difficulties as during original installation. Even if readjustment is not necessary, maintenance is needed for keeping the control system in precise mechanical adjustment, for example, due to wear of the cams which actuate the various switches.
The invention is directed to overcoming the disadvantages of known door operator control systems by completely eliminating mechanically actuated position switches, such as closed limit, open limit, and/or reverse override switches, for not only simplifying construction and reducing cost, but also for facilitating installation and reducing required maintenance. Nor is obstruction detection means used to accomplish such a result, but instead an entirely different approach is used. Therefore, there is no reduction in the life of the door operator since no additional mechanical stress is imposed.